When drilling oil and gas wells, it is important to have pressure containment, formation isolation, and well integrity to have a well that is safe and productive. Therefore, it is critical to have casing run to the desired depth and cemented in place in the wellbore to provide an adequate pressure boundary for well integrity. Also, to minimize well construction costs, it is also important to minimize the time needed to run casing to the desired setting depth. Time spent attempting to work past an obstruction, is money wasted. Downhole obstructions can consist of settled cuttings, formation caving due to wellbore instability, mud weight material sag, salt flows, or tar flows. These problems can occur in offshore and onshore wells.
A majority of land based wells drilled in the world are horizontal wells. These types of wells are often drilled quickly, and as a result of the high inclination horizontal production zone pose a particular problem in fully cleaning cuttings from the wellbore. As a result, operators sometimes encounter difficulties in running intermediate and production casing to the bottom of the wellbore. The ability to generate high velocity flow from the bottom of the casing string would greatly help run casing past areas of settled cuttings.
Many deepwater wells in the Gulf of Mexico as well as some extended reach wells drilled from land based rigs experience zones with tar that can seep into the newly drilled wellbore, making it difficult to run casing through these areas.
There have been numerous attempts to deal with adverse downhole conditions through a variety of casing shoe designs. The ‘shoe’ is the bottom most section of a wellbore casing. Some of the existing methods include reamers or cutting structure located on the shoe, methods of allowing or forcing the shoe to rotate, and blunt guides to allow the casing to traverse obstructions.
There are ‘jetting’ shoes available, but these ‘jetting’ shoes need very large flow areas to be able to allow displaced fluid to enter the casing, and to circulate cement and large particulate lost circulation material (LCM) to be pumped through the shoe. Often, the large bore center nozzle remains, and additional ‘nozzles’ are drilled facing downhole or up hole to provide some additional directed flow. As a result, the total flow area is far too large to provide a true high velocity flow stream that would have any effect on downhole obstructions as mentioned above. Some reamer shoes do have some smaller nozzles, but they also have limited ability to circulate cement or LCM if these nozzles become plugged rendering them vulnerable and ineffective in many circumstances.
Also there currently exists no means to work casing through areas of tar. Often casing will not be able to work through tar flows because of the above requirements for a large flow area required to allow fluid to flow in from the bottom of the casing as a result of the fluid displaced by the casing while running into the hole. If there is a large ‘surge’ effect caused by pressure buildup at the bottom of the wellbore, this could result in fracturing the formation and causing loss of well control. Therefore, ‘auto-fill’ casing float equipment creates a large flow area to allow the fluid to enter the casing unobstructed. Consequently a need exists for a casing shoe that addresses the drawbacks of existing designs and resolves the problems previously unaddressed with running casing.